Release material delivery system

Abstract: A fuser apparatus for heat fusing toner images to print substrates, comprising an elongated fuser roll (34) and an elongated pressure roll (36). The pressure roll is supported for pressure engagement with the fuser roll to form a nip (65) therebetween adapted to receive substrates (82). An oil impregnated web material (77) and an elongated pinch roll (79) are provided. The pinch roll (79) has an outer surface mounted against the web material (77) to urge the web material into contact with the fuser roll (34) to apply release material to the fuser roll. The outer surface of the pinch roll (79) is of an open celled foam material, and is of greater diameter in the central portion of the roller than at the end portions. The pinch roll thus applies a greater pressure to the web (77) over the central portion than at the end portions, and therefore applies more release material over the central portion of the fuser roll than over its end portions.

Description: The present invention relates to an apparatus for applying offset preventing liquid to the fuser roll of a fuser apparatus according to the preamble of claim 1. In imaging systems commonly used today, a charge retentive surface is typically charged to a uniform potential and thereafter exposed to a light source to thereby selectively discharge the charge retentive surface to form a latent electrostatic image thereon. The image may comprise either the discharged portions or the charged portions of the charge retentive surface. The light source may comprise any well known device such as a light lens scanning system or a laser beam. Subsequently, the electrostatic latent image on the charge retentive surface is rendered visible by developing the image with developer powder referred to in the art as toner. The most common development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the charge retentive surface to form a powder image thereon. This toner image may be subsequently transferred to a support surface such as plain paper to which it may be permanently affixed by heating or by the application of pressure or a combination of both. In order to fix or fuse the toner material onto a support member or substrate permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the substrate or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the substrate. One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the substrate to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. Typical of such fusing devices are two roll systems wherein the fusing roll is coated with a compliant material, such as a silicone rubber or other low surface energy elastomer or, for example, tetrafluoroethylene resin sold by E. I. DuPont De Nemours under the trademark Teflon. In these fusing systems, however, since the toner image is tackified by heat it frequently happens that a part of the image carried on the supporting substrate will be retained by the heated fuser roller and not penetrate into the substrate surface. The tackified toner may stick to the surface of the fuser roll and offset to a subsequent sheet of support substrate or offset to the pressure roll when there is no sheet passing through a fuser nip resulting in contamination of the pressure roll with subsequent offset of toner from the pressure roll to the image substrate. To obviate the foregoing toner offset problem it has been common practice to utilize toner release agents such as silicone oil, in particular, polydimethyl silicone oil, which is applied to the fuser roll surface to a thickness of the order of about 1 µm to act as a toner release material. These materials possess a relatively low surface energy and have been found to be materials that are suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser nip and thereby prevents toner from adhering to the fuser roll surface. Various systems have been used to deliver release agent fluid to the fuser roll including the use of oil soaked rolls and wicks with and without supply sumps as well as oil impregnated webs. With these various systems, a uniform amount of release fluid can be applied to the surface of the fuser roll. When the copy substrate dimension normal to the direction of travel of the substrate is less than the total length of the fuser roll, the ends of the roll beyond the copy paper (i.e. the portions of the roll surface not contacted by the copy paper) continuously take on oil without removal thereof, while the area contacted by the copy paper has some of the oil removed by the copy paper as it moves through the nip between the fuser roll and pressure roll. The foregoing results in a build-up of release oil at the ends of the fuser roll, causing swelling of the ends of the roll to such a degree that the fuser roll and/or pressure roll coating weakens and blowout occurs resulting in paper handling problems and fuser roll and/or pressure roll failure. US-A-5,045,890 discloses a fuser apparatus for applying offset preventing liquid to a fuser roll including:a supply core; a rotatable take-up core; an oil impregnated web member adapted to be moved from the supply core to the take up core; a motor mechanically coupled to the take up roll for driving the web member from the the supply core to the take up core; a pressure roll in engagement with the web member and positioned to provide a contact nip for the web member with the fuser roll opposite the pressure roll wherein the contact of the web member with the fuser roll transfers oil from the web member to the fuser roll, and a controller to vary the duty cycle of operation of the motor to drive the web member at a relatively constant linear speed at the contact nip, the controller including a timer to monitor the cumulative time of operation of the motor to progressively decrease the duty cycle of the motor in response to the cumulative time of operation wherein the progressively decreased duty cycle of operation compensates for the increasing radius of the web member on the take up roll to maintain the relatively constant linear speed at the contact nip. Additionally, there are several automatic printing machines commercially available, such as the Xerox 5028 model copier, which employ webs for providing release agents to fuser rolls. Other examples of such commercial devices, presently or currently available, include the Canon model 3225, 3725, 3000 series, 4000 series and 5000 series products. "Xerox" and "Canon" are registered trade marks. These products also all have liquid release agent impregnated webs supported between a supply roll and a take-up roll and urged into contact with the fuser roll by an open celled foam pinch roll. GB-A-2,017,538 discloses a donor roll for applying release liquid directly to a fuser roll. The donor roll is made from either copper or steel and tapers from one end to the other. In accordance with one aspect of the present invention there is provided apparatus for applying offset preventing liquid to a fuser roll comprising: a web material having offset preventing liquid impregnated therein; and an elongated pinch roll of open cell foam material having an outer surface mounted in engagement with said web material to urge said web material into contact with the fuser roll to apply the offset preventing liquid to the fuser roll, characterised in that said pinch roll has a first uniform diameter over a first region to apply a first pressure over a first region of the web material and a second uniform diameter over a second region contiguous to the first region to apply a second pressure over a second region of the web material, so that the web material applies a greater amount of offset preventing liquid to the fuser roll over the first region than over the second region. Pursuant to another aspect of the present invention there is provided an apparatus for fusing toner to a print substrate, comprising a fuser roll and a pressure-roll. The fuser roll and the pressure roll form a nip with the fuser roll adapted to receive the substrate. A web material having offset preventing liquid impregnated therein and an elongated pinch roll of open cell foam material is provided. The elongated pinch roll has an outer surface mounted in engagement with the web material to urge the web material into contact with the fuser roll to apply the offset preventing liquid to the fuser roll. The pinch roll has a first uniform diameter over a first region to apply a first pressure over a first region and a second uniform diameter over a second region contigous to the first region to apply a second pressure over a second region in the web so that the web applies a greater amount of offset preventing liquid to the fuser roll over the first region than over the second region. Other aspects of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: Figure 1 is a schematic elevational view, partially in section, showing the features of the release material delivery system of the present invention therein; Figure 2 is an enlarged elevational view of the pinch roll used in the Figure 1 delivery system; Figure 3 is a profile of the pressure applied by the pinch roll of the present invention on a web material; and Figure 4 is a graph showing the test results with the pinch roll of the present invention, and a uniform diameter pinch roll installed in an electrographic printing machine. Attention is now directed to Figure 1 from which the invention will be explained in greater detail. Specifically, a heat and pressure fuser apparatus 33, including a web release agent delivery system therefor are schematically illustrated. As shown in Figure 1, the fuser apparatus 33 comprises a heated fuser roll 34 which is composed of a core 54 having coated thereon a thin layer 56 of an elastomer. The core 54 may be made of various metals such as iron, aluminum, nickel, stainless steel, etc., and various synthetic resins. Aluminum is preferred as the material for the core 54, although this is not critical. The core 54 is hollow and a heating element 58 is generally positioned inside the hollow core to supply the heat for the fusing operation. Heating elements suitable for this purpose are known in the art and may comprise a quartz heater made of a quartz envelope having a tungsten resistance heating element disposed internally thereof. The method of providing the necessary heat is not critical to the present invention, and the fuser member can be heated by internal means, external means or a combination of both. Heating means are well known in the art for providing sufficient heat to fuse the toner to the support. The thin fusing elastomer layer may be made of any of the well known materials, for example, RTV and HTV silicone elastomers. The fuser roll 34 is shown in a pressure contact arrangement with a pressure roll 36. The pressure roll 36 comprises a metal core 62 with a layer 64 of a heat-resistant material. In this assembly, both the fuser roll 34 and the pressure roll 36 are mounted on bearings (not shown). The pressure roll bearings are mechanically loaded,as schematically indicated by the arrow 80 so that the fuser roll 34 and pressure roll 36 are pressed against each other under sufficient pressure to form a nip 65. It is in this nip that the fusing or fixing action takes place with toner images 81 on a substrate 82 contacting the heated fuser roll 34. The layer 64 may be made of any of the well known materials such as fluorinated ethylene propylene copolymer or silicone rubber. It is preferred that the fuser and the pressure roll used in conjunction with this invention are of the type described in copending EP-A-0,606,143. That is, both the fuser roll and the pressure roll have crown profiled engaging surfaces to form a substantially uniform nip across their lengths and provide a substantially constant nip force and a substantially uniform velocity profile to sheets passing through the nip. However, it will also be understood that the present invention can be used in conjunction with a wide variety of fuser configurations needing a delivery of release fluid to the fuser apparatus. The liquid release agent delivery or management system 71 of the present invention comprises a housing 73 containing release agent material (not shown) for example, silicone oil. The silicone oil is applied to the surface of the fuser roll 34 via a web of material 77 which is impregnated with the oil and which is drawn from supply 76 to a take up roll 78. The web material 77 is impregnated with silicone oil and upon contact with the fuser roll 34, it delivers silicone oil thereto. The web material 77 contacts the fuser roll at a nip formed between the fuser roll 34 and a pinch roll 79 formed of an open cell material for applying a thin coating of silicone oil thereon for preventing offset of images carried by a paper substrate. The liquid release agent may be selected from those materials which have been conventionally used. Typical release agents include a variety of conventionally used silicone oils including both functional and non-functional oils. Thus, the release agent is selected to be compatible with the rest of the system. It is preferred that the release agent delivery system 71 be of the type disclosed and discussed in copending EP-A-0,606,135. Various other systems have been used to deliver release agent fluid to the fuser roll including the use of oil soaked rolls and wicks with and without supply sumps as well as oil impregnated webs. Another type of release agent system is disclosed in US-A 4,214,549 issued to Rabin Moser on July29, 1980. As disclosed therein, release agent material is contained in a sump from which it is dispensed using a metering roll and a donor roll, the former of which contacts the release agent material and the latter of which contacts the surface of the heated fuser roll. The supply roll 76 and take-up roll 78 are made from interchangeable rotatable tubular support cores 80 to enable the reversibility of the web. The supply roll core 80 has a supply of release agent impregnated web material 80 wound around the core and is back tensioned within the housing to resist unwinding by suitable means. The take-up roll 78 is mounted for rotation in the counterclockwise direction (as viewed in Figure 1) in order to transport the web 77 onto it. While the web is illustrated as being moved in the the "against" direction relative to the fuser roll 34 it will be appreciated that it could also be moved in the "with" direction. Suitable bearings, gears and a motor (not shown) are provided to advance the impregnated web 77 from the supply roll 76 to the take-up roll 78. The system 71 may be fabricated in accordance with the system disclosed in U.S. Patent Nos. 5,045,890 and 5,049,944. The foam pinch roll 79 is spring biased toward the fuser roll by two coil springs 86 (only one being shown), one at each end of the pinch roll mounting slot to apply pressure between the web 77 and the fuser roll 34 to ensure delivery of an adequate quantity of release agent to the fuser roll and cleaning thereof. The open cell foam pinch roll may be made of any suitable material which is resistant to high temperatures of the order of the fusing temperature at 225°C and does not take a permanent set. Typically, it is a molded silicone rubber foam with open cells about 0.5 millimeters in their maximum dimension to enable the storage of release agent. As shown in Figure 2, the diameter at each end region of the pinch roll is less than the diameter of the center region of the roll, resulting in pressure between the web 77 and the fuser roll 34 being less at each end region thereof as shown in Figure 3. Figure 3 is a pressure profile of the pinch roll of the present invention on the web with equal loads X and Y, respectively, on the two ends of the pinch roll. Preferably, loads X and Y are loaded to the fuser roll with a force of about 6,6 N (0.68 Kg). If the force is less than about 6,6 N (0.68 Kg) the web does not wrap correctly on the take-up roll resulting in premature failure. It has been found that minimizing the pressure applied on the web material along the edges of the web which is in contact with the fuser roll reduces the amount of release agent supplied to each end region of the fuser roll. These end regions are outside the area of contact corresponding to that which would be contacted by the width of the most used copy paper (e.g. a 279 mm wide copy paper) moving through the nip formed by the fuser roll and pressure roll. In the foregoing manner, release agent is applied in a greater amount to the area of the surface of the fuser roll which is contacted by the most used copy paper. Accordingly, release agent is applied in a lesser amount beyond the edges of the most used copy paper of the roll, allowing sufficient cleaning of rolls when wider, less frequently used, copy paper is employed. This reduces swelling and blow out of each end of the fuser roll and /or pressure roll to increase the life of the fuser roll and pressure roll An electrophotographic printing machine was tested (1) with the pinch roll of the present invention installed and (2) with a pinch roll of uniform diameter Reference is now made to Figure 4, which is graphical representation on the data collected in the testing of the two pinch rolls showing the changing diameter of a pressure roll versus copy count during an end of life test with various web configurations. Line 1A and Line 1B represent the present invention. In this embodiment the pinch roll was approximately 310 mm long, the central region had a diameter of 20mm, one end region had a diameter of 15 mm and a length of 10 mm, and the other end region had a diameter of 15 mm and a length of 20 mm The pressure roll of line 1A had an initial diameter of 28.640 mm and was tested with a short web. It was found that the pressure roll of line 1A failed at 331K copies. The pressure roll of line 1B had an initial diameter of 28.720 mm and was tested with a full web. It was found that the pressure roll of line 1B failed at 324K copies. Line 2A and Line 28 represent pinch rolls with a uniform diameter. In this embodiment the pinch roll was approximately 310 mm long with a diameter of 20 mm The pressure roll of line 2A had an initial diameter of 28.665 mm and was tested with a short web. It was found that the pressure roll of line 2A failed at 242K copies. The pressure roll of line 2B had an initial diameter of 28 630 mm and was tested with a full web. It was found that the pressure roll of line 2B failed at 164K copies. In recapitulation, there has been described an apparatus for applying offset preventing liquid to a fuser roll, comprising a web material having offset printing liquid impregnated therein. An elongated pinch roll of open cell foam material having an outer surface mounted in engagement with the web material to urge the web material into contact with the fuser roll to apply the offset preventing liquid to the fuser roll. The pinch roll has a first uniform diameter over a first region to apply a first pressure over a first region and a second uniform diameter over a second region contigous to the first region to apply a second pressure over a second region in the web so that the web applies a greater amount of offset preventing liquid to the fuser roll over the first region than over the second region.

Claims: Apparatus for applying offset preventing liquid to a fuser roll (34) comprising: a web material (77) having offset preventing liquid impregnated therein; and an elongated pinch roll (79) of open cell foam material having an outer surface mounted in engagement with said web material (77) to urge said web material into contact with the fuser roll (34) to apply the offset preventing liquid to the fuser roll (34), characterised in that said pinch roll (79) has a first uniform diameter over a first region to apply a first pressure over a first region of the web material (77) and a second uniform diameter over a second region contiguous to the first region to apply a second pressure over a second region of the web material (77), so that the web material (77) applies a greater amount of offset preventing liquid to the fuser roll (34) over the first region than over the second region. The apparatus of claim 1, wherein the first region of said pinch roll (79) comprises a central portion thereof, and the second region of said pinch roll (79) comprises opposed marginal end portions. The apparatus of claim 2, wherein the central portion of said pinch roll (79) comprises a greater diameter than the opposed marginal end portions thereof. The apparatus of claim 3, wherein one of the opposed marginal end portions extends in a longitudinal direction a length greater than that of the other opposed marginal end portion of said pinch roll (77). The apparatus of claim 4, wherein the opposed marginal end margins are of substantially equal diameters. An apparatus for fusing toner (81) to a print substrate (82), comprising : a fuser roll (34); a pressure-roll (36), forming a nip (65) with said fuser roll (34) adapted to receive the substrate (82); and means for applying offset preventing liquid to the fuser roll (34) comprising the apparatus of any one of claims 1 to 5.

Inventors: DEBOLT FREDERICK C, GHEER BARRY J, RASCH KENNETH R, DEBOLT, FREDERICK C., GHEER, BARRY J., RASCH, KENNETH R.,
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1994
Main classification: G03G15
IPC codes: G03G15, B05C1